The geophysical strand of the DART project will be investigating the extent to which monthly seasonal variations affect the conditions ideal for the detection of archaeological residues. This is mainly dependant on the contrast between the target archaeology and the surrounding soil matrix. Past studies based on monthly surveying over archaeological features (Clark, Hesse, Cott) have shown there to be a seasonal variation associated with geophysical detection which is a function of soil geology, the weather, temperature etc. The DART project aims to continue to explore the effect of these variables on test sites with differing geologies and archaeological features.
Past studies into the effects of seasonal variation have however, led to variable results, and have not investigated the instantaneous effect of weather on the measurements, which is vital to the understanding of the accuracy of the measurements. Surprisingly perhaps, the author does not recall work looking at the effect of the immediate weather on survey success. This is key to investigate, because if the results show a large variation in survey success over the days of a month, the validity of once-monthly surveys would be drastically affected, and the dependency we have on the results collected once a month is thrown into question. The investigations will also help highlight the dynamic action of moisture variation through the soil, and how quickly (and if) periods of wet weather effect geophysical readings, and for how long.
The proposed method will be to set up a test area at the University of Bradford. This will be used as a survey platform for a month. Each day of the month the test area will be surveyed with earth resistance and GPR measurements, using a twin-probe array at resolution of 0.5X0.5m. Resistivity pseudosections (or ERT) will also be conducted over the site. This will provide a dataset of approx. 30 surveys which will be analysed. It will be important to obtain local, accurate weather information on a day-to-day basis so that this data can be cross-referenced with the geophysical datasets.
Andy Parkyn has already conducted monthly seasonality tests over a test area at Bradford University and logistically it would seem sensible to continue this work, using this same test area, and his local expertise.
Subtle variation is expected throughout the month, with occasional peaks in the datasets following conditions of adverse rainfall. It is expected that a small trend will be plotted over the duration of the month. This study will highlight a practical need for deeper understanding into the immediate impact of local weather on moisture variation over a site.